Dyntopo Sculpting questions?
You should only use Dynamic Topology if you make major changes to your mesh, especially if you want to expand an area out effectively changing the necessary Topology. Also you should avoid using Dyntopo if you use UVs and never use it with Subsurface on a mesh, because it works with triangles instead of quads.

For Example if you have a Cube and you want to add details on it you could do it with dyntopo if you don't bother with UVs Vertex Colors and Modifiers like the Subsurface Modifier  but if you want to use any of it its not recommended. UVs can of course be added later on in the process but that more difficult for a triangle mesh than for a quad mesh (at least in my opinion). But there aren't only negatives to Dyntopo. For Example you want to make that same Cube but for a Game. Then it needs to have the least amount of triangles possible. Dyntopo adds only vertices where you need them, where the other way of doing it with a Multiresolution Modifier would add a lot of vertices everywhere to get the same level of detail, while keeping the topology. Also you could only use dyntopo if you want to sculpt something like a human from just a cube, because you don't have the correct topology for a human in a Cube